Low Ouput Voltage From Voltage Regulator IC
I have two Big 40″ dell LCD screens with the same fault. The 12.8vdc supply to the the three fans has a voltage drop to 7.5 V. They are fed from an KIA278 R12PI. With fans disconnected the voltage reads 12.8 V dc. as I add the fans one at a time the voltage starts to drop. After running for 20 minutes the over temperature alarm comes up. I have checked all the surrounding components and they seem ok. Is it possible that it could be the R12PI? I have about 20 of these units running.
The KIA278R12PI is a 4 terminals 2 ampere voltage regulator IC. Pin 1 is the DC input and pin 2 is the DC output. Pin 3 is the ground and pin 4 is On/off control. In your case, the problem could be due to the voltage regulator IC itself or the DC supply input have problem. With the fan running the DC supply input should have about 15 to 16 volt and above. If you get less than that this means the DC supply source could have problem like bad electrolytic capacitor.
First you direct replace the IC and retest. If the problem still the same then check on the DC supply voltage. Below is the link to the IC: